1. Field of the Invention
The present invention relates to a new and more efficient absorption solution for removing acidic impurities, such as CO.sub.2 and/or H.sub.2 S, from gaseous mixtures containing them.
2. Description of the Prior Art
As is known, the removal of the said impurities is effected by an absorbing solution is a so-called absorption stage; the exhausted solution is then renewed, with expulsion of the impurities previously absorbed, in a so-called regeneration stage.
In the hitherto known art, the said absorbing solutions have been chosen from solutions containing an alkali metal carbonate or an alkali metal phenate, borate or phosphate, or alkali metal salts of aminoacids, and from solutions of ethanolamines, mainly MEA, DEA and TEA, which are also much used.
These solutions contain essentially a substance of a basic nature which effects the quantitative absorption of CO.sub.2. It is known that when this basic substance is an alkali metal carbonate, the rate of absorption is very low and the solution is difficult to use in practice in industry. This drawback has been overcome by the addition to the absorption solution, of activating substances such as those listed below, which increase the initial rate of absorption of the CO.sub.2, which is then chemically linked to the alkali metal carbonate, thus improving the the overall absorbing power of the solution.
It should be recalled in this connection that it was at first proposed to use potash solutions activated with aminoacids (glycine), patented in 1954, and subsequently to use as activating substances As.sub.2 O.sub.3 and compounds of selenium and tellurium, these uses also being patented in 1954. Subsequently there was proposed the addition of ethanolamines (the use of which had been suggested as long ago as 1936 in "Carbon Dioxide" by Quinn and Jones), and particularly DEA, the use of which was patented in 1964 and 1965, and lastly the use of the borate of ethanolamine was suggested and subsequently patented.
Here it will be noted briefly that the aforesaid activating substances are divided into two categories: As.sub.2 O.sub.3 has a catalytic effect on the reaction of CO.sub.2 with water, in the sense that the reaction (called the hydration of CO.sub.2) is greatly promoted. On the contrary the substances with amino groups (such as the aminoacids and ethanolamines) have a CO.sub.2 -carrying property, in the sense that they absorb the CO.sub.2 with a very high reaction rate, thus facilitating the passage of the CO.sub.2 into the liquid phase.